1. Field of the Invention
This invention relates to a process for improving the mechanical properties of metal, and particularly to a process for producing a magnesium composite having a rapidly solidified metal matrix and a reinforcing phase.
2. Description of the Prior Art
A magnesium based composite generally comprises two components--a magnesium alloy matrix and a hard reinforcing second phase. The composite typically exhibits at least one characteristic reflective of each component. For example, a magnesium based metal matrix composite should have the low density of the magnesium matrix and the high elastic modulus of the reinforcing phase. Magnesium based metal matrix composites fabricated to date are made by mixing a reinforcing phase with molten magnesium and then ingot casting. This technique does provide a composite, but the mixing technique employed does not result in a uniform distribution of reinforcement, and is limited by the mechanical and physical properties of the magnesium based alloy matrix. As a result, the mechanical properties may be anisotropic and the composite itself may demonstrate poor corrosion resistance. It has been proposed that these techniques and associated limitations be avoided by solid state bonding/mixing (e.g., mechanically alloying) the matrix with the addition of the particular reinforcement. This procedure permits the reinforcing phase to be mixed and bonded to the matrix without heating the material to a temperature above the solidus of the matrix. Prior processes in which magnesium based alloys and/or metal matrix composites are mechanically alloyed by means of solid state bonding are disclosed in U.S. Pat. Nos. 4,264,362, 4,017,414, 3,993,577 and 3,942,511. In those processes intimate mixing of magnesium with various elemental additions by mechanical alloying was utilized to create micro electrochemical cells for the purpose of promoting corrosion without regard to the mechanical integrity of the final product form. The present invention provides a material having enhanced mechanical properties and improved corrosion resistance.